Albert Mestres

Knowledge-Defined Networking

The research community has considered in the past the application of Artificial Intelligence (AI) techniques to control and operate networks. A notable example is the Knowledge Plane proposed by D.Clark et al. However, such techniques have not been extensively prototyped or deployed in the field yet. In this paper, we explore the reasons for the lack of adoption and posit that the rise of two recent paradigms: Software-Defined Networking (SDN) and Network Analytics (NA), will facilitate the adoption of AI techniques in the context of network operation and control. We describe a new paradigm that accommodates and exploits SDN, NA and AI, and provide use-cases that illustrate its applicability and benefits. We also present simple experimental results that support, for some relevant use-cases, its feasibility. We refer to this new paradigm as Knowledge-Defined Networking (KDN).

Time-Domain Analysis of Graphene-Based Miniaturized Antennas for Ultra-Short-Range Impulse Radio Communications

Graphene is enabling a plethora of applications in a wide range of fields due to its unique electrical, mechanical, and optical properties. Among them, graphene-based plasmonic miniaturized antennas (or shortly named, graphennas) are garnering growing interest in the field of communications. In light of their reduced size, in the micrometric range, and an expected radiation frequency of a few terahertz, graphennas offer means for the implementation of ultra-short-range wireless communications. Motivated by their high radiation frequency and potentially wideband nature, this paper presents a methodology for the time-domain characterization and evaluation of graphennas. The proposed framework is highly vertical, as it aims to build a bridge between technological aspects, antenna design, and communications. Using this approach, qualitative and quantitative analyses of a particular case of graphenna are carried out as a function of two critical design parameters, namely, chemical potential and carrier mobility. The results are then compared to the performance of equivalent metallic antennas. Finally, the suitability of graphennas for ultra-short-range communications is briefly discussed.

Time- and Frequency-Domain Analysis of Molecular Absorption in Short-Range Terahertz Communications

Graphene is enabling a plethora of applications in a wide range of fields due to its unique electrical, mechanical, and optical properties. In this context, graphene antennas are envisioned to enable ultra-high-speed wireless communication in short transmission ranges, due to both their reduced size and their radiation frequency in the terahertz band. Despite its high potential bandwidth, the terahertz band presents several phenomena that may impair the communication and reduce the achievable data rate. In this letter, the phenomenon of molecular absorption is quantitatively analyzed, evaluating the scalability of both time- and frequency-domain performance metrics with the transmission distance. The results of this analysis show that molecular absorption creates a tradeoff between the achievable throughput and the maximum transmission distance at which short-range terahertz wireless communications can successfully take place.

Scalability of Broadcast Performance in Wireless Network-on-Chip

Networks-on-Chip (NoCs) are currently the paradigm of choice to interconnect the cores of a chip multiprocessor. However, conventional NoCs may not suffice to fulfill the on-chip communication requirements of processors with hundreds or thousands of cores. The main reason is that the performance of such networks drops as the number of cores grows, especially in the presence of multicast and broadcast traffic. This not only limits the scalability of current multiprocessor architectures, but also sets a performance wall that prevents the development of architectures that generate moderate-to-high levels of multicast. In this paper, a Wireless Network-on-Chip (WNoC) where all cores share a single broadband channel is presented. Such design is conceived to provide low latency and ordered delivery for multicast/broadcast traffic, in an attempt to complement a wireline NoC that will transport the rest of communication flows. To assess the feasibility of this approach, the network performance of WNoC is analyzed as a function of the system size and the channel capacity, and then compared to that of wireline NoCs with embedded multicast support. Based on this evaluation, preliminary results on the potential performance of the proposed hybrid scheme are provided, together with guidelines for the design of MAC protocols for WNoC.

Scalability of the Channel Capacity in Graphene-Enabled Wireless Communications to the Nanoscale

Graphene is a promising material which has been proposed to build graphene plasmonic miniaturized antennas, or graphennas, which show excellent conditions for the propagation of Surface Plasmon Polariton (SPP) waves in the terahertz band. Due to their small size of just a few micrometers, graphennas allow the implementation of wireless communications among nanosystems, leading to a novel paradigm known as Graphene-enabled Wireless Communications (GWC). In this paper, an analytical framework is developed to evaluate how the channel capacity of a GWC system scales as its dimensions shrink. In particular, we study how the unique propagation of SPP waves in graphennas will impact the channel capacity. Next, we further compare these results with respect to the case when metallic antennas are used, in which these plasmonic effects do not appear. In addition, asymptotic expressions for the channel capacity are derived in the limit when the system dimensions tend to zero. In this scenario, necessary conditions to ensure the feasibility of GWC networks are found. Finally, using these conditions, new guidelines are derived to explore the scalability of various parameters, such as transmission range and transmitted power. These results may be helpful for designers of future GWC systems and networks.

Multicast On-chip Traffic Analysis Targeting Manycore NoC Design

The scalability of Network-on-Chip (NoC) designs has become a rising concern as we enter the many core era. Multicast support represents a particular yet relevant case within this context and has been the focus of different research efforts, mainly due to the poor performance of NoCs in the presence of this increasingly important type of traffic. However, most of the proposed schemes have been evaluated using synthetic traffic or within a full system, which is either unrealistic or costly. While traffic models would allow to better assess their performance, existing proposals do not distinguish between unicast and multicast flows and often are bound to a given number of cores. In this paper, a trace-based multicast traffic characterization is presented with the aim to provide guidelines for the modeling of multicast communications in many core settings. To this end, the scaling trends of aspects such as the multicast traffic intensity or the spatiotemporal injection distribution are analyzed. The novelty of this work resides both on its scalability-oriented approach and on the use of correlation metrics to evaluate potential prediction opportunities.

Initial MAC Exploration for Graphene-enabled Wireless Networks-on-Chip

In the upcoming many-core era, chip multiprocessor architectures will be composed of hundreds or even thousands of processor cores, which interact among them through an on-chip communication platform for synchronization and data coherency/consistency purposes. As the traffic generated within the chip becomes more multicast-intensive, it is necessary to conceive novel communication platforms that go beyond conventional schemes and guarantee multicast support with high throughput, low latency, and low power. Nanotechnology provides an opportunity within this context by virtue of terahertz graphene antennas, which could allow the integration of one antenna per core in a Graphene-enabled Wireless Network-on-Chip (GWNoC). However, it is essential to design an appropriate MAC protocol in order to fully benefit from this novel approach. To provide a first contribution in this direction, in this paper we design two baseline MAC protocols based on the well-known ALOHA and carrier sensing techniques. Their functionalities have been properly conceived by taking into account characteristics and requirements of future chip multiprocessors systems. Moreover, their performances have been evaluated by means of computer simulations under different chip configurations. Obtained results demonstrate the pros and cons of these simple contention-based MAC protocols and pave the way for the future exploration of the MAC design space.

A MAC protocol for Reliable Broadcast Communications in Wireless Network-on-Chip

The Wireless Network-on-Chip (WNoC) paradigm holds considerable promise for the implementation of fast and efficient on-chip networks in manycore chips. Among other advantages, wireless communications provide natural broadcast support, a highly desirable feature in manycore architectures yet difficult to achieve with current interconnects. As technology advancements allow the integration of more wireless interfaces within the same chip, a critical aspect is how to efficiently share the wireless medium while reliably carrying broadcast traffic. This paper introduces the {Broadcast, Reliability, Sensing} protocol (BRS-MAC), which exploits the particularities of the WNoC context to meet its stringent requirements. BRS-MAC is flexible and employs a collision detection and notification scheme that scales with the number of receivers, making it compatible with broadcast communications. The proposed protocol is modeled and evaluated, showing a clear latency advantage with respect to wired on-chip networks and WNoCs with token passing.

Evaluating the Feasibility of Wireless Networks-on-Chip Enabled by Graphene

Network-on-Chip (NoC) is currently the paradigm of choice for covering the on-chip communication needs of multicore processors. As we reach the manycore era, though, electrical interconnects present performance and power issues that are exacerbated in the presence of multicast communications due to the point-to-point nature of NoCs. This dramatically limits the available design space in terms of manycore architecture, sparking the need for new solutions. In this direction, the use of wireless interconnects has been recently proposed as a complement of a wired plane. In this paper, the concept of Graphene-enabled Wireless Network-on-Chip (GWNoC) is introduced, which extends the native broadcast capabilities of existing wireless NoCs by enabling the per-core integration of antennas that radiate in the terahertz band (0.1 - 10 THz). Preliminary results on the feasibility of GWNoC are presented, covering implementation, on-chip networking and multiprocessor architecture aspects.

Fundamentals of Graphene-Enabled Wireless On-Chip Networking

In the broad sense of the term, nanonetworks may refer not just to networks composed of nanosized devices, but also to communication networks enabled by nanotechnology. Nanoscale communication techniques can be suitable to interconnect elements far larger than a few square micrometers in applications subject to strong size constraints or bandwidth requirements. Here, the concept Graphene-enabled Wireless Network-on-Chip (GWNoC) is introduced as a clear example of this category. In GWNoC, graphene plasmonic antennas are used to wirelessly communicate the components of a multicore processor, which are located in the same chip. This shared medium approach is opposed to current chip communication trends and aims to reduce many of the issues that hamper the development of scalable multiprocessor architectures. In this chapter, we describe the scenario and the communication requirements that justify the employment of nanonetworking techniques, as well as the main challenges that still need to be overcome in this new research avenue.